Rheostat



F. A. ROJAS June 12, l 923.

RHEOSTAT Filed Nov. 18 1921 A TTORNE Y Patented June 12, 1923.

UNITED STATES FLORICEL A. BO-TAS, OF NEW YORK, N. Y.

BHEOSTAT.

Application filed November 18, 1921. Serial No. 516,135.

To alZ whom it may concern Be it known that I, F LORICEL A. Home, a citizen of the Re ublic of Santo Domingo, residing at New ork city, in the county of Bronx, State of New Iork, have invented certain new and useful Improvements in Rheostats; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

The invention relates to rheostats of the compressible resistance type. The resistance'element of such rheostats consists in general of a fibrous non-conducting material, such as asbestos, impregnated with a powdered conducting substance such as graphite and held between two relatively movable members. As these members are moved toward each other the materialis compressed and its resistance decreased. As

the members .are moved apart the material is expanded and its resistance increased. In accordance with my Patents Nos. 1,315,579, September 9,1919, and 1,366,95, February 1, 1921, the relatively movable members are in the form of conducting plates or electrodes to which resistance material is secured and is thus positively expanded as well as compressed by a movement of the plates, no reliance being placed upon the resiliency of the material itself to effect expansion.

Such rheostats would serve admirably for dimming individual electric lamps and controlling the current in small electrical attachments could they be adapted for use within standard sockets. It is accordingly an object of the present invention to adapt rheostats of this type for use within standard electric light sockets.

In my application, Serial No. 516,134 filed concurrently herewith, I have disclosed a rheostat of the compressible resistance type mounted within a standard electric ,light socket. In the form shown in that application the lamp or attachment plug is screwed within its seat in the customary manner, and remains stationarv during use. A longitudinally movable, screw-threaded collar electrically connected with the seat which, as usual, forms one of the external contacts, bears upon the movable plate of the rheostat, making electrical contact therewith, and by its movement compresses the resistance material.

It is a further object of this invention to provide simpler means for moving the movable plate of the rheostat. The movable screw-threaded collar is accordingly eliminated and the rheostat so designed that movement of the plate and compression of the resistance material is effected by the longitudinal movement of the lamp or attachment plug within its screwthreaded seat. One means for efl'e'cting the control in this manner is illustrated in the accompanying drawings in which Fig.1 is

a vertical section through a socket and its rheostat; Fig. 2 is a vertical section taken along line 2-2 of Fig. 1 and at 90 to the section shown in Fig. 1; Figs. 3, t and 5 are transverse sections taken along lines 33, 4 1 and 55 respectively of Fig. 1; and Figs. 6, 7, and 8 are detail views of parts which will be described later.

The socket itself, which is of standard size and form, is indicated in the drawings by reference numeral 1. The socket is provided at its lower end with the usual base cup 2, adapted to be screwed upon a sup porting terminal 3, from which the two. leads 4 and 5 extend, and at its outer end with a threaded seat 6 for an attachment. A lamp 7 has been shown and the operation of the rheostat will be described in connection with a lamp, but its use is, of course, not so limited. This seat 6 forms one of the electrical contacts with the lamp and is insulated from the socket by means of a cylindrical wall of insulating material 8. 'llhe foregoing is common construction and 15 found in practically every electric light socket. I

in accordance with this invention a rheostat is mounted within the socket and placed in series with the lamp. The resistance element of this rheostat comprises a compressible mixture of asbestos fibres and conducting powders which shall be discussed in detail later. It is indicated by the reference numeral 9 and is held between two relatively movable metal plates 11 and 12 and within a container 13, preferably of enameled iron. container of enameled metal has been found best adapted, for not only is it heat-resistant and non-conducting, but its walls can be made very thin and hence occupy a minimum of valuable space. It also has a certain flexibility and can adaptitseli to slight variations of the other parts from standard size. The container 13 and the lower plate 12 are supported upon a base 14 held within the base of the socket and made of some insulating and heat-resisting material, preferably porcelain. The container 13, although of general cylindrical form, is provided at one side with a recess 15 extending radially inward and beyond the vertical axis of the container, as is clearly shown in Fig. 6. The function of this recess is to house the other lead and a shunt, which is thrown in parallel with the resistance when the conductivity of the latter approaches full current capacity, and to insulate them com pletely from the resistance material. The up 1' plate 11 is shaped to fit around the wall s of recess 15 and is designed to side relative thereto, Secured to the upper face of plate 11 is a block of porcelain 16 111(6- wise shaped to move over the walls of the recess 15. To the upper face of this block of porcelain 16 is secured a plate 17 electrically connected with the ,plate 11 by means of screws 18.

Resting upon the lower plate 12' and within the recess 15 is a block of porcelain 19 held in position by means of a metallic pin 21 passing through the base 14 and secured to a terminal plate 22. The pin 21 also extends through an opening in an extension 27 on the seat 6. The block of porcelain 19 is provided as shown in Figs. 1, 2 and 7 with a passageway 23 concentric with the axis of the socket. Into this passageway extends a screw 24 which projects upwardly through .the base 14 and is secured to a terminal plate 25. Extending downwardly into passageway 23 is a metallic pin 26 secured to plate 17. Surrounding this pin and concentric therewith is an expansion coil spring 28 which bears upon the lower face of plate 17 and the block of porcelain 19.

I have found that a mixture of equal parts asbestos fibre and graphite forms a satisfactory resistance material but one which'after long usage deteriorates because of slow consumption of the graphite particles. I have found that the addition of about two per cent of copper powder and a small quantity of calcium carbonate checks this consumption and prolongs the life of the rheostat. I have also found that the material immediately adjacent the movable plate is expanded to a greater extent than that adjacent the stationary plate. This results in overheat-in of this material adjacent the movable p ate. This objection can be overcome by making that part of the material adjacent the movable plate richer in the conducting element; about seven parts graphite to four of asbestos being a satisfactory proportion. I have also discovered that the resistance material adheres best to plates of iron.

The operation of the device acting as an electric light dimmer is as follows: When the lamp 7 is in position as shown and the leads 4: and 5 connected to a source of electrical energy, the path of the current is through lead 4, plate 22, pin 21, extension 27, seat 6, the lamp, plate 17 pins 18, plate 11, resistance material 9, plate 12, screw 24:, plate 25 and lead 5. As is well understood, the conductivity of the resistance material varies directly with its density. If, therefore, the lam 7 is screwed farther within its seat the block of porcelain 16 and plate 11 are moved downwardly, compressing the resistance material and decreasing its resistance. This means that more and more current is allowed to pass through the lamp and the light grows brighter and brighter. Continuing the movement of the lamp in a downward direction the point is reached when'pin 26 and screw 24 contact. This immediately shunts the current through these elements and makes it unnecessary for the resistance to carry the whole load. By adjusting the space between the end of these two parts relative to the resistance of material 9, the shunt can be thrown in at such a time that the conductivity of the compressed resistance material is allowin practically enough current to flow for 111 luminosity. This means that when the shunt is thrown in a small flicker results, which indicates that full current is flowing. This flicker is only slight and unobjectionable and is not a jump, as would be the case were the resistance 9 considerably greater when contact is made. When the rheostat is used to regulate the current flowing through the filament of an electric lamp, the flicker is probabl sufficient indication that full current is owing. When, however, the attachment is an iron or some device which does not give visible indications of the current flowing through it, means should be provlded which shall be audible indication. One such means comprises a small metallic washer 29 which lies upon block 19 and concentric with passageway 22. This washer is provided with a small extension 30 which pro ects into the line of travel of pin 26. TlllS pin is provided with a notch 31 which engages the projection 30 when the shunt has been or is about to be thrown in, and a snap results which is distinctly audible.

To decrease the luminosity of the lamp 1t 1s only necessary to reverse the movement. As the lamp moves upwardly the block 16 and plate 11 follow it under the influence of spring 28. The block 16 is provided with a shoulder which abuts against the lower ends of seat 6 and insulating material 8 and thus limits the upward movement of plate 11.

made the resistance of material 9 should be increased to such a point that the light is barely glowing and is, therefore, very gently extinguished.

There is, of course, the usual heat loss when current passes through the compressible resistance material, the loss being at its maximum when the conductivity of the resistance equals that of the external resistance, such as a lamp filament. For high and low resistances this loss is very little. Even at its maximum, however, the heat generated is successfully radiated, so that the heating of the socket is not excessive. Nevertheless, I have found it best to provide the leads 4 and 5 with an asbestos covering for the first few inches of their length. This heating of the resistance material expands it, increases the contact among the conducting particles, and thus decreases the resistance of the whole. In my Patent 1,366,945, I have disclosed certain' thermostatic means for compensating for this change in resistance. In the present structure the enamelled iron container 13 acts as a thermostat, and with rise in temperature tends to close in upon recess 15 and increase the volume of the resistance material. This change can be made to compensate for the expansion of the resistance material and the resulting decrease in its resistance.

This rheostat has been successfully mounted within a standard electric light socket. In spite of the limited space the rheostat has been provided with a shunt, completely insulated from the resistance material, which is thrown in when the resistance of the resistance material has been lowered to a predetermined point. Means are also provided for positively breaking the current flow when the-resistance has been increased to a predetermined point. The device is very simple in operation; the compression of the compressible resistance material being efi'ected by the movementof the lamp or attachment lug within its seat. As an electric light immer this rheostat is peculiarly efficient but its use is, of course, not limited to this.

One particular embodiment has been shown and described, but it is recognized that certain structural changes might be made without departing from the true spirit of the invention.

w I claim:

1. In an electric light socket designed to seat an attachment plug, the combination of i a compressible resistance rheostat within the socket and forming a part thereof, and means for compressing the resistance material of the rheostat by means of the plug.

2. In an electric light socket designed to seat an attachment plug, the combination of a compressible resistance rheostat within the socket and forming a part thereof, and means for controlling the compression of the resistance material of the rheostat by movement of the plug within its seat. 3. In an electric light socket designed to seat an attachment plug, the combination of a compressible resistance material held between two relatively movable plates within the socket and forming a part thereof, the arrangement of the parts being such that movement of the plug within its seat effects a movement of one of the plates to vary the density and resistance of the resistance material.

4. In an electric light socket, the combination of a compressible resistance material held between a stationary plate and a movable plate within the socket and forming a part thereof, a seat for an attachment plug, an extension on the movable plate extending within the seatand designed to make electrical contact with the center contact of the plug, the arrangement f the parts being such that movement of the plug compresses the resistance material.

5. In an electric light socket designed to seat an attachment plug, the combination of a rheostat comprising a compressible resistance material held between'two relatively movable parts within the socket and independent of the plug, and means constantly urging theplates apart to expand the material, movement of the plates toward each other being effected by movement of the plug within its seat.

6. In an electric light socket designed to seat an attachment plug, the combination of a rheostat comprising a compressible resistance material held between a stationary plate and a movable plate within the socket and independent of the plug, means constantly urging the the material, and means limiting the outward movement of the movable plate, inward movement of the movable plate being effected by the movement of the plug within its seat.

In testimony whereof I allix my si ature.

FLORICEL A. R JAS.

plates apart to expand 

